Patent Application
20110252810
The invention generally relates to refrigeration, and more specifically, to a standing wave thermoacoustic piezoelectric refrigerator for refrigeration by utilizing standing acoustic waves.
Thermoacoustic engines are commonly used as heat pumps or refrigerators, they utilize energy associated with thermoacoustic waves for refrigeration process.
In existing technologies, usually thermoacoustic refrigerators utilize energy associated with the thermoacoustic waves to transfer heat from a lower temperature end to a higher temperature end. Such thermoacoustic refrigerators use transducers as acoustic drivers for utilizing the acoustic energy. Further, the thermoacoustic refrigerators use a hot heat exchanger and a cold heat exchanger. A porous structure may be configured between the hot heat exchanger and the cold heat exchanger. The porous structure is made up of one or more of metal foils, a metal mesh, a sheet of a foamed metal, and sheets of filter paper. Additionally, the thermoacoustic refrigerators may include one or more moving parts and moving masses to generate the thermoacoustic waves. These one or more moving parts and moving masses require sliding seal mechanisms for their operation. The thermoacoustic waves may be generated within the thermoacoustic refrigerators using mechanism used for generating sonic waves. The thermoacoustic waves thus generated are utilized to trigger the heat from the lower temperature end to the higher temperature end.
Further, a free piston mechanism may be used to reduce complexities in using the one or more moving parts and moving masses in the thermoacoustic refrigerators to generate the thermoacoustic waves. The free piston mechanism in the thermoacoustic refrigerators utilizes gas springs to generate thermoacoustic waves. The gas springs in the thermoacoustic refrigerators work similar to mechanical pistons, thereby, partially eliminating the need of sliding seal mechanisms. However, the use of moving masses in the thermoacoustic refrigerators is still required in such thermoacoustic refrigerators.
Therefore, there is a need for a system for efficiently performing refrigeration process using thermoacoustic energy.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.
Before describing in detail embodiments that are in accordance with the invention, it should be observed that the embodiments reside primarily in combinations of apparatus components related to a standing wave thermoacoustic piezoelectric refrigerator. Accordingly, the apparatus components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
Generally speaking, pursuant to various embodiments, the invention provides a standing wave thermoacoustic piezoelectric refrigerator. The standing wave thermoacoustic piezoelectric refrigerator includes a housing. The housing includes a compressible fluid. Additionally, the housing has a first portion and a second portion. Further, the standing wave thermoacoustic piezoelectric refrigerator includes a porous stack within the housing. The porous stack is positioned between a hot heat exchanger and a cold heat exchanger within the housing. The standing wave thermoacoustic piezoelectric refrigerator also includes a piezoelectric bimorph at an end of the first portion of the housing. The piezoelectric bimorph is configured opposite to an end of the first portion having the porous stack. The piezoelectric bimorph is capable of oscillating to generate acoustic energy upon receiving energy from an external energy source. Due to the oscillation of the piezoelectric bimorph the compressible fluid compresses and expands within the housing. This enables the compressible fluid to traverse between the first portion and the second portion through the porous stack to generate standing acoustic waves. The standing acoustic waves enable the compressible fluid to transfer heat from the cold heat exchanger to the hot heat exchanger.
Referring to drawings and in particular to
Additionally, a cross-sectional shape associated with one or more of first portion 106 and second portion 108 may be one of a circle, a square, a rectangle, and a polygon. For example, in a scenario, first portion 106 may have a tapered configuration with a circular cross section and second portion 108 may have a tapered configuration with a circular cross section. Alternatively, first portion 106 and second portion 108 may have a different configuration and cross-sectional shape. For example, first portion 106 may have a straight configuration and a rectangular cross-sectional shape, and second portion 108 may have a tapered configuration and a circular cross-sectional shape.
Standing wave thermoacoustic piezoelectric refrigerator 100 may further include a porous stack 112. Porous stack 112 may include one or more of, but are not limited to, metal foils, a metal mesh, a sheet of a foamed metal, and a sheet of filter paper. Porous stack 112 is positioned between a hot heat exchanger 114 and a cold heat exchanger 116 within housing 102. For example, porous stack 112 may be configured such that hot heat exchanger 114 is positioned near one end of porous stack 112 and cold heat exchanger 116 is positioned near another end of porous stack 112 opposite to the end of porous stack 112 where hot heat exchanger 114 is positioned. Hot heat exchanger 114 is configured within second portion 106. In an embodiment, hot heat exchanger 114 may be at an ambient temperature. Cold heat exchanger 116 is configured within first portion 108. Hot heat exchanger 114 and cold heat exchanger 116 facilitates in creation of a temperature gradient between first portion 106 and second portion 108 within housing 102.
Further, standing wave thermoacoustic piezoelectric refrigerator 100 includes a piezoelectric bimorph 118 at an end of first portion 106. Piezoelectric bimorph 118 is configured at an end of first portion 106 opposite to an end of first portion 106 where porous stack 112 is configured. Piezoelectric bimorph 118 oscillates upon receiving energy from an external energy source. The external energy source may include one of, but not limited to, electrical energy and solar energy. Piezoelectric bimorph 118 may be oscillated by an existing system known in the art. The existing system may be capable of utilizing the external energy source to oscillate piezoelectric bimorph 118. Thus, the amount of oscillation of piezoelectric bimorph 118 may be based on the amount of energy supplied by the external energy source. For example, in an instance, frequency of oscillations of piezoelectric bimorph 118 may be increased by increasing the frequency of energy supplied to piezoelectric bimorph 118. In another instance, intensity of oscillations of piezoelectric bimorph 118 may be increased by increasing amount of energy supplied to piezoelectric bimorph 118.
Due to the oscillation of piezoelectric bimorph 118, compressible fluid 104 compresses and expands within housing 102. Compressible fluid 104 traverses between first portion 106 and second portion 108 through porous stack 112 in response to the compression and expansion of compressible fluid 104. Thereafter, a cyclic transformation takes place inside compressible fluid 104. The cyclic transformation includes compression, heating, expansion, and cooling of one or more of fluid parcels of compressible fluid 104 within housing 102. A cyclic transformation of the one or more fluid parcels in a standing wave thermoacoustic piezoelectric refrigerator is explained in detail in conjunction with
The cyclic transformation of compressible fluid 104 results in the generation of two acoustic waves, such as, an acoustic wave 120 and an acoustic wave 122 as shown in
An instance of the standing acoustic waves within standing wave thermoacoustic piezoelectric refrigerator 100 is illustrated in
In an embodiment, frequency associated with the standing acoustic waves generated within first portion 106 may be changed based on dimension of one or more of first portion 106 and second portion 108. The dimension of first portion 106 includes one or more of, but not limited to, configuration of first portion 106, cross-sectional shape of first portion 106, and length of first portion 106. Similarly, the dimension of second portion 108 includes one or more of, but not limited to, configuration of second portion 108, cross-sectional shape of second portion 108, and length of second portion 108. For example, frequency of standing acoustic waves in a standing wave thermoacoustic piezoelectric apparatus having a long first portion may be less as compared to frequency of standing acoustic waves in a standing wave thermoacoustic piezoelectric apparatus having a short first portion.
In an embodiment, the energy supplied by the external energy source to piezoelectric bimorph 118 may be varied to generate the standing acoustic waves in first portion 106 of housing 102. For example, in an instance, the temperature level of cold heat exchanger 116 may start increasing, thereby resulting in a need to further cool cold heat exchanger 116. This increase in temperature of cold heat exchanger 116 may also result in slow down of refrigeration process. To decrease the temperature of cold heat exchanger 116, standing acoustic waves of high intensity are generated. The high intensity standing acoustic waves may be generated by increasing the energy supplied by the external energy source to piezoelectric bimorph 118. This high intensity standing acoustic waves facilitates in transfer of heat from cold heat exchanger 116 to hot heat exchanger 114 thereby accelerating the refrigeration process.
In another embodiment, the energy supplied by the external energy source to piezoelectric bimorph 118 may be varied based on a threshold oscillation frequency of piezoelectric bimorph 118. The threshold oscillation frequency is associated with a resonating frequency of first portion 106 of housing 102. For example, the threshold oscillation frequency indicates a frequency associated with first portion 106 of the housing for generating a quarter cycle of the standing acoustic waves. However, it will be apparent to a person skilled in the art that the threshold oscillation frequency of the housing may indicate a frequency for generating any number of cycles of the standing acoustic waves.
In still another embodiment, temperature associated with hot heat exchanger 114 may be varied to generate the standing acoustic waves in first portion 106 of housing 102. For example, the temperature level of hot heat exchanger 114 may increase upon receiving heat from cold heat exchanger 116. This may result in heat transfer from hot heat exchanger 114 to one or more fluid parcels of compressible fluid 104 near hot heat exchanger 114. When the one or more fluid parcels travel towards cold heat exchanger 116, heat may traverse an area near hot heat exchanger 114 to an area near cold heat exchanger 116. To decrease the traversal of heat from hot heat exchanger 114 to cold heat exchanger 116, temperature within hot heat exchanger 114 may be decreased. The decrease in temperature of hot heat exchanger 114 reduces temperature difference between hot heat exchanger 114 and cold heat exchanger 116. This may in turn reduce a need of high intensity standing acoustic waves to transfer heat from cold heat exchanger 116 to hot heat exchanger 114.
In an embodiment, temperature associated with cold heat exchanger 116 may be varied to generate the standing acoustic waves in first portion 106 of housing 102. For example, the temperature level of cold heat exchanger 116 may start increasing, thereby resulting in need of further cooling of cold heat exchanger 116. This increase in temperature of cold heat exchanger 116 may also result in slow down of refrigeration process. This may also result in a need of standing acoustic waves of high intensity to transfer heat from cold heat exchanger 116 to hot heat exchanger 114. To trigger the refrigeration process, the temperature within cold heat exchanger 116 is decreased. This may reduce the need of high intensity standing acoustic waves to transfer heat from cold heat exchanger 116 to hot heat exchanger 114.
In another embodiment, the temperature of compressible fluid 104 may be varied to generate the standing acoustic waves within first portion 106 of housing 102. The temperature of compressible fluid 104 may be varied by varying temperature of surrounding of standing wave thermoacoustic piezoelectric apparatus 100. For example, in order to match the frequencies of the two acoustic waves travelling in opposite direction, the temperature of surrounding is increased to generate the standing acoustic waves within first portion 106.
Standing wave thermoacoustic piezoelectric refrigerator 100 uses piezoelectric bimorph 114 and includes fixed parts for the refrigeration process. The use of such fixed parts eliminates the need of sliding seal mechanisms. Further, referring back to optimally shaped configuration of one or more of first portion 106 and second portion 108 of standing wave thermoacoustic piezoelectric refrigerator 100, a tapered configuration of one or more of first portion 106 and second portion 108 increases the intensity of the standing acoustic waves generated in first portion 106 and second portion 108. This reduces the need of high frequency oscillation of piezoelectric bimorph 118 for creating high intensity standing acoustic waves.
Turning now to
The cyclic transformation of fluid parcel 200 takes place based on oscillation of a piezoelectric bimorph such as, piezoelectric bimorph 118 within the standing wave thermoacoustic piezoelectric refrigerator such as, standing wave thermoacoustic piezoelectric refrigerator 100. The oscillation of the piezoelectric bimorph is triggered upon receiving energy from an external energy source. This is explained in detail in conjunction with
Due to the oscillation of the piezoelectric bimorph, the cyclic transformation of the compressible fluid takes place. During the cyclic transformation, the compressible fluid traverses between a first portion such as, first portion 106 and a second portion such as, second portion 108 of a housing such as, housing 102 of standing wave thermoacoustic piezoelectric refrigerator 100. Based on the oscillation, when the piezoelectric bimorph moves inward, one or more fluid parcels of the compressible fluid near the piezoelectric bimorph pushes the compressible fluid away from the piezoelectric bimorph. This results in compression of fluid parcel 200 inside the housing at stage 204. The compression of fluid parcel 200 decreases the volume of fluid parcel 200 and increases the pressure of fluid parcel 200. This reduction in the volume and increase in the pressure is indicated by stage 204 as shown in P-V diagram 202. At stage 206, fluid parcel 200 collects heat in response to the compression of fluid parcel 200. This results in heating of fluid parcel 200 at a constant volume. The heating of fluid parcel 200 is indicated by stage 206 as shown in P-V diagram 202. At this stage, the pressure of fluid parcel 200 is maximum and a velocity of fluid parcel 200 is negligible.
Meanwhile, as the piezoelectric bimorph moves outward based on the oscillation of the piezoelectric bimorph, the one or more fluid parcels of the compressible fluid near the piezoelectric bimorph pulls the compressible fluid towards the piezoelectric bimorph. This results in expansion of fluid parcel 200 inside the housing at stage 208. The expansion of fluid parcel 200 decreases the pressure of fluid parcel 200 and increases the volume of fluid parcel 200. This reduction in the pressure and increase in the volume is indicated by stage 208 as shown in P-V diagram 202. Thereafter, at stage 210, fluid parcel 200 dispatches heat in response to the expansion of fluid parcel 200. This results in cooling of fluid parcel 200 at constant volume. The cooling of fluid parcel 200 is indicated by stage 210 as shown in P-V diagram 202. At this stage, the pressure of fluid parcel is minimum and the velocity of fluid parcel is negligible. Subsequently, the piezoelectric bimorph again moves inwards based on the oscillation. This further result in compression of fluid parcel 200 in the housing similar to stage 204. As a result, the cyclic transformation of fluid parcel 200 occurs within the standing wave thermoacoustic piezoelectric refrigerator.
During the cyclic transformation inside the compressible fluid, the compression and expansion of the one or more fluid parcels of the compressible fluid results in back and forth movement of the one or more fluid parcels along the standing wave thermoacoustic piezoelectric refrigerator. The back and forth movement of the one or more fluid parcels generate two acoustic waves within the housing. The two acoustic waves travel in opposite directions as one acoustic wave of the two acoustic waves is a reflection of another acoustic wave of the two acoustic waves. When the frequencies of the two acoustic waves match, standing acoustic waves are created within the first portion of the housing. This is explained in detail in conjunction with
Referring now to
Due to the standing acoustic waves, fluid parcel 300 traverses between the cold heat exchanger to the hot heat exchanger through the porous stack of the standing wave thermoacoustic piezoelectric refrigerator. The standing acoustic waves enables one or more fluid parcels of the compressible fluid present near the cold heat exchanger to push fluid parcel 300 thereby decreasing the volume of fluid parcel 300. These one or more fluid parcels may have maximum velocity when they are travelling away from the cold heat exchanger. Thereafter, fluid parcel 300 starts traveling towards the hot heat exchanger from the cold heat exchanger. This results in compression of fluid parcel 300 at stage 304. The compression of fluid parcel 300 decreases the volume of fluid parcel 300 and increases the pressure of fluid parcel 300. This reduction in the volume and increase in the pressure is indicated by stage 304 as shown in P-V diagram 302 in
Further, when the standing acoustic waves pulls one or more fluid parcels of the compressible fluid near the cold heat exchanger, volume of fluid parcel 300 starts increasing. In this case, the one or more fluid parcels of the compressible fluid may have maximum velocity while traveling towards the cold heat exchanger. Thereafter, fluid parcel 300 starts traveling towards the cold heat exchanger. This results in expansion of fluid parcel 300 at stage 308. The expansion of fluid parcel 300 increases the volume of fluid parcel 300 and decreases the pressure of fluid parcel 300. This increase in the volume and reduction in the pressure is indicated by stage 308 as shown in P-V diagram 302. Towards the end of stage 308 temperature of fluid parcel 300 is lower as compared to temperature of the walls of the porous stack near fluid parcel 300. At stage 310, fluid parcel receives heat from one or more of the cold heat exchanger and the walls of the porous stack. This results in heating of fluid parcel 300 and cooling of the cold heat exchanger. The heating of fluid parcel 300 is indicated by stage 310 as shown in P-V diagram 302. In the meanwhile, the standing acoustic waves again push fluid parcel 300 towards the hot heat exchanger from the cold heat exchanger similar to stage 304. As a result, a cyclic transformation of fluid parcel 300 occurs inside the porous stack within the standing wave thermoacoustic piezoelectric refrigerator. This cyclic transformation of one or more fluid parcels within the porous stack contributes to the refrigeration process.
Various embodiments of the invention provide a standing wave thermoacoustic piezoelectric refrigerator for refrigeration process. The standing wave thermoacoustic piezoelectric refrigerator uses a piezoelectric bimorph. As a result, the frequency of oscillation of the piezoelectric bimorph is easily controlled to trigger the refrigeration process. Further, the standing wave thermoacoustic piezoelectric refrigerator uses piezoelectric bimorph along with fixed parts thereby eliminating the need of sliding seal mechanisms. Moreover, one or more of a first portion and a second portion of the standing wave thermoacoustic piezoelectric refrigerator may have tapered configuration. The tapered configuration facilitates in increasing the intensity of the standing acoustic waves generated in the first portion thereby reducing the amount of energy required to oscillate the piezoelectric bimorph.
Those skilled in the art will realize that the above recognized advantages and other advantages described herein are merely exemplary and are not meant to be a complete rendering of all of the advantages of the various embodiments of the invention.
In the foregoing specification, specific embodiments of the invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
